1. Field of the Invention
The present invention relates to the field of image display technologies, and specifically, to a TFT array substrate, particularly a capacitor for a TFT array substrate, a method of manufacturing the capacitor, and a shift register comprising the capacitor, a gate driver array substrate and a display device.
2. Description of the Related Art
A progressive scanning matrix display in an M×N dot matrix is employed in an image display panel comprising an array substrate for controlling a light source. Taking a TFT-LCD (thin film field effect transistor liquid crystal display) for an example, drivers of the array substrate mainly comprises a gate driver (scan driver) and a data driver, wherein an inputted clock signal, after converted by a shift register, is applied by the gate driver to a gate line of a liquid crystal display panel.
Shift registers are often used in gate drivers of a liquid crystal display panel, and each gate line is connected with one stage of circuit units of the shift register. Gate input signals are output by a gate drive circuit, so that respective pixels are scanned line by line. The gate drive circuit may be provided on the display panel in a packaging way such as COF (Chip On Film) or COG (Chip On Glass), or the gate drive circuit may be formed by TFTs (thin film field effect transistor) into an integrated circuit unit and formed in the display panel. For the liquid crystal display panel, a GOA (Gate On Array) design of a gate driver enables a reduction of production cost, a removal of one process step, and an increase in yield.
Generally, a shift register of a gate driver of a TFT-LCD is consisted of several TFTs and capacitors. FIG. 1 is schematic diagram showing a cascade configuration of a shift register of a TFT-LCD gate driver in prior arts. As can be seen from FIG. 1, a signal inputted at an input end Input of each stage of the shift register SR is a signal outputted from an output end Output of a previous stage of the shift register SR; an output signal at a reset end Reset of each stage of the shift register SR is a signal outputted from an output end Output of a next stage of the shift register SR. As such, the GOA-based gate drive circuit of the liquid crystal display can be turned on line by line, thereby achieving display of a screen.
FIG. 2 is a schematic diagram showing stages of a shift register in prior arts. As shown in FIG. 2, the shift register SR comprises a plurality of TFTs M1˜M13 and a capacitor C1. With an increasing market demand in narrow frame design, development of narrow frame design is restricted more and more by a size of the shift register, especially a size of the capacitor, thus optimization of the size of the shift register has become an urgent matter at present. Currently, there are many existing technologies for optimizing and reducing the number of TFTs. Capacitor(s), however, is a necessary basic unit of a shift register and thus is indispensable. Further, there is at least one capacitor in a shift register, and a capacitance of the capacitor is at least from several picofarads (pf) to dozens of picofarads, that is, an area occupied by the capacitor is generally from 1,000 μm2 to 1,000,000 μm2. In general, when manufacturing a shift register of a gate driver of a TFT-LCD, a TFT gate layer may be used to form one electrode of capacitor, and a TFT source-drain layer may be used to form other electrode of the capacitor. Typically, TFT gate layer and TFT source-drain layer are made of a metal and are not transparent.
For almost all of current products, since the frame thereof is relatively narrow, there is a overlapped portion between a frame sealing glue and a GOA region; since the frame is relatively narrow, the frame sealing glue is substantially blocked and covered by a black matrix (BM) at a side of a CF (Color Filter), and UV cure of the frame sealing glue can only be performed from the TFT side, at this time, it is required that the capacitor is designed into a hollowed-out form so that UV light can pass therethrough so as to cure the sealing glue.
If an increased space for the hollowed-out design of a capacitor for the ultraviolet cure of the frame sealing glue is taken into account, the area of the capacitor needs to be increased by about 50%, which will significantly impacts the size of the frame. Generally, an product based on ADS (Advanced Super Dimension Switch) technology is manufactured by a liquid crystal process comprising sequentially forming a TFT gate layer, a gate insulation layer, a first ITO layer (pixel electrode), a TFT active layer, a TFT source-drain layer and then a TFT passivation layer, and finally a second ITO layer (common electrode).
Generally, when manufacturing a shift register of a gate driver of a TFT-LCD, a TFT gate layer may be used to form one electrode of capacitor, and a TFT source-drain layer may be used to form other electrode of the capacitor. At this time, a structure of the capacitor is shown in FIGS. 3A and 3B.
FIGS. 3A and 3B respectively show a capacitor design without being overlapped with a frame sealing glue and a capacitor design overlapped with a frame sealing glue. As shown in FIGS. 3A and 3B, an existing capacitor is consisted of a TFT gate layer 2, a gate insulation layer 3 and a TFT source-drain layer 4 sequentially formed on a glass substrate 1.
In such a case, a thickness of the gate insulation layer 3 between the TFT source-drain layer 4 and the TFT gate layer 2 is about 4,000 Å˜5,000 Å; further, since the TFT gate layer 2 and TFT source-drain layer 4 are made of a non-transparent metal material, the TFT gate layer 2 and the TFT source-drain layer 4 need to be designed into a hollowed-out form when considering curing of the frame sealing glue. If it is intended that the capacitance of the capacitor remains unchanged and opposite area between the TFT gate layer 2 and TFT source-drain layer 4 cannot be reduced, the space occupied by the capacitor needs to be increased, thereby ensuring magnitude of the capacitance.